Rebecca Howlett recently got in touch to share her thoughts about the use of Ginkgo Biloba in the prevention of Acute Mountain Sickness. Here's what she wrote...
What if there was a drug that worked better than acetazolamide in preventing acute mountain sickness (AMS)? Something that had fewer side effects and was available "over the counter"? Sounds like a winner? Ginkgo Biloba has been used for decades to prevent AMS and many believe it's the real deal. But is it good enough to knock acetazolamide off its pedestal?
Acetazolamide, commonly known as Diamox, will be well known to anyone who's headed to high altitude. Through its diuretic effects it increases the excretion of bicarbonate from the kidneys and creates a metabolic acidosis that stimulates ventilation and increases the supply of oxygen to the body's tissues. Great, the perfect solution! Unfortunately side effects are common and sometimes they're not dissimilar to the effects of AMS itself. Whilst “prevention is better than cure” is it worth taking a drug that makes you sicker than if you developed the very disease you're trying to prevent?!?
What's the alternative? Let’s step into the realm of herbal medicine and see what's about. Ginkgo Biloba (GB) (also knowns as Maidenhair Tree) was first identified as something that could prevent AMS back in 1996.
Ginkgo Biloba (also known as Maidenhair Tree). Despite little supportive scientific evidence, the leaf extract is widely used to treat a range of conditions including dementia, hypertension and macular degeneration. The amount of active ingredient varies widely between preparations and makes comparisons between studies difficult to make
A recent meta-analysis that examined the effect of GB upon AMS prevention identified a total of 7 randomised controlled trials (RCT's). Overall, the researchers found that amongst the 451 participants included in the trials, the incidence of AMS was 32% (72/223) in the GB group compared to 46% (104/228) in the placebo group. Whilst a 30% reduction sounds impressive, this didn't reach statistical significance and it should be said that the largest study (326 participants) showed that AMS was in fact commoner amongst those taking GB!
The evidence to support the use of acetazolamide is much clearer. In a meta-analysis of 17 RCT's and 2,322 participants, researchers showed that the incidence of AMS was 16% in the acetazolamide group and 33% in the placebo group. The 48% reduction was statistically significant and led the authors to conclude, "acetazolamide is effective prophylaxis for the prevention of AMS symptoms in those going to altitude".
To date, PHAIT (Prevention of High-Altitude Illness Trial) is the largest study to directly compare the effect of acetazolamide and GB on AMS prevention. Randomising 487 participants on a trek to Lobuje (4928m), researchers showed that the incidence of AMS was 12% (14/118) in those taking acetazolamide and 35% (43/124) in those taking GB. Whilst there was a clear statistical difference between these 2 drugs there was no difference between GB and placebo 34% (40/119).
A rash triggered by a sulfonamide drug. Since acetazolamide is a sulfonamide derivative, blood disorders, rashes, and other sulfonamide-related side-effects can occasionally occur. Users should be told to report any unusual skin rashes
PHAIT's results also go some way to providing us with information about the side effects of both drugs. Both seemed well tolerated. Drop out rates and missed doses did not differ between acetazolamide, GB and placebo. Whilst urinary frequency, taste disturbance and paraesthesia were commoner in those taking acetazolamide, side effects such as blurred vision and rash were rare.
The best way to avoid AMS is to ascend slowly and cautiously. Most people don't need drugs to help them along the way. But if you're one of those people who thinks they need to take something GB is not the answer. Stick with acetazolamide. It hasn't been knocked off its pedestal yet!
Rebecca Howlett is a 4th year medical student and one of the current presidents of Cardiff WEMS. She grew up in the Yorkshire Dales and Tanzania and had the luxury of having hills and mountains as her playground – although at the age of 4 she wasn’t quite ready to summit Kilimanjaro and so a photo next to it had to do!