These include any hormone-based drugs, like the contraceptive pill and some fertility medicines, and drugs used to prevent heart attack and stroke. Antihistamines should also not be used to help passengers sleep during a flight.

What makes flying different from other forms of travel?

While flying is one of the safest forms of travel, there are specific risks that come with air travel, regardless of the length of the flight.

Passenger planes are typically pressurised to the same atmospheric conditions that are found at 10,000 feet altitude. At that level, the effective oxygen level is only 14.3%, which is much lower than the 20.9% found at ground level.

An additional risk is reduced blood flow from a lack of movement and sitting in cramped conditions, unless of course you’re fortunate enough to be in business or first class. And finally, dehydration is also a common side effect of flying due to the lack of humidity in the air.

When these conditions are combined, it results in an increased risk of deep vein thrombosis, which is also known as DVT. This is a type of blood clot that occurs in the veins deep in the body and occurs most often in the legs. The development of a blood clot can result in blocked blood flow to the lungs, heart, or brain, which in turn can cause a heart attack or stroke.