Assessing Travelers' Knowledge and Use of Coca for Altitude Sickness

To the Editor

Many South American nationals chew the coca leaf or drink coca tea either to increase their sensation of energy or to abate the symptoms of altitude sickness. The leaf comes from the coca shrub (Erythroxylum coca) and contains cocaine. ¹ It is known that 75% of the Bolivian population living at and above 4000 m chew coca leaves, although only 20% are habitual chewers at 2400 m and only 3% at sea level. ² Although anecdotal, this is probably the reason that many of the mountaineering community use coca themselves. We would like to share the results of a medical student project investigating the epidemiology of coca use among the overland traveling population and their opinions, reasons, and beliefs about coca and its use.

A convenience sample of the overland traveling population at high altitude tourist destinations in Peru and Bolivia was taken. These included Machu Picchu, Lake Titicaca, and La Paz. We included all those older than 18 years of age. We excluded people who did not understand English and, to exclude habitual coca users, those of South American nationality. We distributed 160 questionnaires made up of 15 closed questions. The survey identified demographic information including age, gender, nationality, and the altitude experienced. It identified whether coca was used, the reasons for why, and whether it was used specifically as a prophylactic or treatment for altitude sickness. The questionnaire asked about the effects of coca, dependence on coca, and knowledge of the constituents of coca. A section for additional comments was provided at the end of the questionnaire. The study was granted exemption from the London (Wandsworth) regional ethics committee.

Of the 160 people approached, 136 (84%) completed the questionnaire. One hundred twenty-one of 136 (89%) subjects took coca. There were an equal number of males and females. The mean age was 26 years, and all subjects had traveled to higher than 3100 m. Within the coca-taking population, 67 of 121 (55%) exclusively took coca tea, 26 of 121 (22%) exclusively chewed the leaf, and the remaining 28 of 121 (23%) took both. Of those who took coca, 51 of 121 (42%) reported that they took it to prevent altitude sickness, 27 of 121 (22%) reported they took it to treat the symptoms of altitude sickness, and the remaining 43 of 121 (36%) denied using it for altitude sickness. Reasons for not taking it were taste, recommendation to avoid it, no opportunity to take it, and because of its contents and possible effects. Most common reasons for taking coca were personal choice, local guide advice, wanting to take part in local culture, and curiosity. Only 29 of 136 (21%) reported that they knew the constituents of coca tea. Interestingly 51% reported coca had no noticeable effect. Thirty percent reported desirable effects including raised mood (19%) and an increased sensation of energy (12%). Nineteen percent reported undesirable effects including tingling lips (13%), nausea (3%), abdominal pain (2%), and reduced mood (1%). No subjects reported any symptoms of withdrawal after stopping taking coca. Neither dependence on coca nor any serious untoward effects were reported.

This survey identified that the vast majority of the studied population took coca while on their present trip. This number was much higher than expected. Reasons for this may include that coca tea is readily available, often given free in hotels and also with meals at restaurant, and is also available commercially. Although more than half of the population used it for altitude sickness, the majority reported that they felt no effect from coca. We were unable to standardize a dose of coca, and thus it may be that they took a subtherapeutic dose. Less than a quarter actually knew the active components of coca. This was much lower than expected as there was much publicity on coca. Taking coca without knowing it contains cocaine may impact on those returning to their countries of residence. There have been reports of unintentional positive doping tests on professional athletes in those traveling from coca-using areas. These may also occur in the general population. ³ Desirable effects of coca include a raised mood and an increased sensation of energy. As this was a subjective study, we could not differentiate the cause of desirable effects.

A Medline search revealed a lack of scientific evidence to support coca's use for altitude sickness. Research has been limited to small sample sizes and has predominantly investigated improved exercise tolerance. Findings have been confused by an apparent difference in response between habitual and nonhabitual coca users. In nonhabitual coca users there appears to be a mixed physiological and metabolic response. There is an increase in oxygen uptake, heart rate, and respiratory gas exchange ratio along with a reduction in insulin secretion at rest. ⁴ Two studies in habitual coca users have been unable to replicate the physiological response but support the metabolic response. They showed reduced precursors of glycolysis and increased fatty acid availability that could be beneficial for prolonged submaximal exercise.^5,6 Just one study has looked at coca and altitude sickness. The sample contained nonhabitual coca users and found significantly lower reports of nausea, headache, and nocturnal dyspnea and significantly higher oxygen saturations when taking coca. ⁷ Much like our study, the conclusions drawn are limited by the subjective nature of the findings and small nonrandomized sample group. Another hypothesis is that the central acting stimulating effects of one of the constituents, cocaine, may also lead to a reduction in symptoms by reducing any perceived effects of altitude sickness. None of this research is able to conclude which constituent is responsible for coca's actions.

This project has many limitations. The sample size is small, and there may be selection bias. As the vast majority of people took coca there is no true control group, making it hard to draw meaningful conclusions. The project is subjective owing to its use of questionnaires rather than objective data. There was no follow-up of the sample group, making conclusions on withdrawal and dependence limited. Symptoms could not be directly linked to coca and may have been attributable to other factors such as drinks high in caffeine concentration.

In conclusion, this project shows that although a very high proportion of travelers took coca tea, only a minority knew its constituents and less than half reported any noticeable effect. We hope that this project stimulates future thought and research into coca and increases awareness of the use of coca among the traveling population and those advising them.