Drugs of Abuse During Breastfeeding

Opioids

Heroin (diacetylmorphine or diamorphine) is the classic opiate of abuse. It is rapidly metabolized in the body to 6-monoacetylmorphine, which is about six times more potent than morphine; 6-monoacetylmorphine is further metabolized to morphine. All three drugs contribute to heroin's effects. Infants whose mothers use heroin have detectable morphine and other metabolites in their urine, stomach contents, and hair.

Heroin use by the nursing mother is sufficient to cause opiate dependence and mitigate infant withdrawal symptoms in the breastfed infant as illustrated by these two interesting cases. An article from 1915 reported a breastfed newborn infant whose mother began using heroin as a snuff for abdominal pain. She continued to use the snuff and became dependent. Her breastfed infant slept excessively, but when awake would curl up with abdominal cramps and cry continuously until breastfed. When the mother was deprived of the drug, the infant would yawn, sneeze, sweat, cry, and have occasional diarrhea. The mother was arrested and the infant was examined by the prison physician. Upon examination, the infant was “pale and flabby looking” with almost colorless lips and pinpoint pupils that did not react to light. The infant slept for most of a day then awoke with sweating and cramps. The infant was treated with paregoric and tincture of nux vomica three times daily. After 4 days of therapy, the infant reportedly appeared more cheerful and had no more signs of cramps. Nux vomica contains strychnine, so it is no longer used in pharmacologic doses, although it is used in homeopathy.

In an article published 100 years later, an 8-year-old girl was brought to a hospital in Iran by her aunt. The girl's mother had used heroin throughout pregnancy and lactation. She continued to breastfeed the child up to the time of admission to prevent heroin withdrawal in the child. The girl had not been enrolled in school to avoid signs of withdrawal. Both mother and child were treated with buprenorphine for opiate dependence.

Infants have died from exposure to opiates in milk. A woman in Tucson, Arizona who was receiving methadone maintenance during and after pregnancy was convicted of first-degree murder in 1997 after her infant developed anoxia and died a day after being admitted to the hospital. In addition to methadone, the mother had begun using heroin postpartum while she was nursing her 7-week-old infant. ⁵

Less information is available on abuse of prescription opiates by nursing mothers. Nevertheless, the well-publicized death of a breastfed infant after codeine was prescribed to a mother who was an ultra-rapid metabolizer of codeine emphasizes the sensitivity of neonates to opiates in breast milk. A review of published cases of adverse reactions in breastfed infants between 2002 and 2014 found that maternal opioids were implicated in 25% of the cases. Codeine, dihydrocodeine, hydrocodone, methadone, oxycodone, and propoxyphene were each implicated. ⁶

Two points to consider involve the time course of opioid use by the mother. A mother who does not use an opioid during pregnancy, but begins to take it postpartum (including those prescribed for postpartum pain) is different from a mother who took an opioid during late pregnancy. In the latter case, the infant will have developed some degree of tolerance to the opioid in utero and tolerate the drug in breast milk better than an opioid-naive infant. Another factor is that for the first few days postpartum, the dose of opioid that the infant receives via milk is low because of the small volume of colostrum. After lactogenesis II, the dose that the infant receives increases markedly. During the first few days postpartum, an opioid-dependent neonate might be more susceptible to neonatal abstinence (depending on the drug's half-life), whereas the opioid-naive neonate might have no signs of opiate effects until lactogenesis II occurs.

The effects of opiate dependence on the rate of breastfeeding vary in different studies. Differences among the studies might be caused by differences in local environments, institutional policies, patterns of maternal support, patient populations, and possibly the drug used for maintenance. A recent study indicates that mothers receiving methadone for abstinence might be less likely to breastfeed than those receiving buprenorphine, although two previous studies found no difference. Regardless, it appears that opioid-abusing mothers are at greater risk of early discontinuation of lactation than other mothers.

Amphetamines

Amphetamines are sympathomimetic stimulants that can pass relatively easily into breast milk. They appear to be well tolerated by the breastfed infants of mothers receiving an amphetamine prescribed in medicinal doses. During maternal amphetamine abuse, the drug is rather persistent in breast milk, with reported half-lives in milk ranging from 7.4 to 30.3 hours in a few mothers in whom sequential milk samples were obtained. In two mothers, methamphetamine became undetectable in breast milk ∼100 hours after the last drug use, which was about one day prior to the mothers' urine becoming negative for methamphetamine. Additionally, amphetamine derived from metabolism of methamphetamine was present in relatively constant concentrations in breast milk.

Few cases of serious adverse effects in infants of amphetamine-abusing mothers have been reported. In one case, a 2-month-old infant whose mother used illicit street methamphetamine by nasal inhalation was found dead 8 hours after a small amount of breastfeeding and ingestion of 120–180 mL of formula. Although the infant's mother was convicted of child endangerment for the use of methamphetamine during breastfeeding, the role that methamphetamine played in the infant's death has been questioned because of the low infant serum methamphetamine concentration and the mother's alleged minimal breastfeeding.

Although serum prolactin is poorly correlated with milk production, pharmacologically lowering prolactin (e.g., with bromocriptine) can lower milk production. In two articles, women with normal physiologic hyperprolactinemia were studied on days 2 or 3 postpartum. Eight received dextroamphetamine 7.5 mg intravenously, six received 15 mg intravenously, and six served as controls. The 7.5 mg dose reduced serum prolactin by 25–32% compared with control, but the difference was not statistically significant. The 15 mg dose significantly decreased serum prolactin by 30–37% after the infusion; however, milk production was not assessed.

The net effect of amphetamine abuse on successful lactation has been evaluated in two studies. A retrospective Australian study found that mothers who used intravenous amphetamines during pregnancy were less likely to be breastfeeding their newborn infants at discharge than mothers who abused other drugs (27% versus 42%). The cause of this difference was not determined. A prospective, multicenter study followed mothers who used methamphetamine prenatally to those who did not. Mothers who used methamphetamine were less likely to breastfeed their infants at hospital discharge than those who did not use methamphetamine. Again, many other factors probably influence this outcome.

Cocaine

Because of its chemical nature, high concentrations of cocaine are found in random breast milk screening in recreational users. Milk cocaine concentrations have varied over 100-fold in these reports. Part of the variation probably depends on the mode of use: smoking, snorting, or injecting the drug. Infants are extremely sensitive to cocaine because the enzymes that inactivate it, especially cholinesterases, are not well developed. A breastfeeding abstinence period of 24 hours has been suggested for women who occasionally use cocaine while breastfeeding, based on the rapid elimination of cocaine by the mother. Of course, the social situation and possible repeated use are concerns in these cases. Two cases below are illustrative of infant effects of maternal cocaine use.

A woman who was breastfeeding her 1-week-old daughter reported using a “dab” of cocaine on her lower gum and nursing her infant with no effect on her infant's behavior or sleep pattern. One week later she used ∼500 mg of cocaine intranasally over a 4-hour period and breastfed five times during this period. Three hours after first ingesting the cocaine, the mother noted that her infant became markedly irritable, had dilated pupils, and began having vomiting and diarrhea. The infant became increasingly irritable and was taken to the emergency room 4 hours later. On examination, the infant was found to be tremulous and irritable with frequent startling after minimal stimulation, and to have high-pitched crying, hyperactive reflexes, mood lability, and hypertension. The infant remained irritable 12 hours after the last cocaine exposure and remained tremulous and easily startled 24 hours after the last exposure. Irritability and tremulousness slowly abated over the subsequent 24 hours. Mild hypertension persisted up to 72 hours after the last cocaine exposure via breast milk.

The mother of a 11-day-old infant applied cocaine powder to her nipples for pain relief. She then breastfed her infant using a breast shield that allowed protrusion of her nipples. Three hours later, she found the infant gasping, choking, and blue. On arrival at the emergency room, the infant was ashen and cyanotic. He had hypertension, tachycardia, shallow breathing, and hypothermia and was in status epilepticus. Seizures resolved in a few hours after treatment and the infant was discharged at 16 days of age with no apparent sequelae. Although the infant's cocaine exposure was not via the drug in breast milk, it illustrates the extreme risk of exposure of young infants to cocaine.

The effects of cocaine use on breastfeeding have not been well studied. Although long-term cocaine use can result in chronic, low-level hyperprolactinemia, the prolactin level in a mother does not correlate well with breastfeeding success and does not take into account social situation. Two studies found that mothers who use cocaine initiate breastfeeding of their infants less frequently than mothers who do not use cocaine.

Hallucinogens

A single case of phencyclidine use has been reported in a lactating woman. Late in pregnancy, she was hospitalized 3 days following a psychotic reaction after smoking phencyclidine. Thirty-six days later she delivered an infant. A breast milk sample was obtained 5 days after that, which was presumably 44 days after smoking phencyclidine. Phencyclidine was still detectable in milk at that time. Effects on the breastfed infant were not reported.

No information is available on hallucinogens such as lysergic acid dimethylamide (LSD), methylenedioxymethamphetamine (MDMA, Ecstasy), mescaline (from peyote), N,N-dimethyltryptamine (from ayahuasca), or psilocybin (from magic mushrooms). These drugs are typically used intermittently rather than daily. In fact, daily use tends to have diminishing effects on the user, even with increasing doses. So they present a different pattern of risk than drugs that are used continuously. Psilocybin is currently being studied as a treatment for depression, so this issue might arise in the future in mothers with postpartum depression.