The national prescribing guidelines followed by GPs (the British National Formulary – BNF) states that all benzodiazepines are ‘contraindicated’ (not allowed) in treatment of phobias (fear conditions, such as fear of flying). It also states that the use of benzodiazepines to treat short-term anxiety is ‘inappropriate’. Benzodiazepines are only licensed for short-term use in a generalised anxiety crisis – but if this is the case for you, you should seek proper care and support for your mental health, and it would not be advisable to go on a flight. Your GP would be taking a significant legal risk by prescribing against these national guidelines.
Diazepam is a sedative, so it makes you sleepier. If an emergency occurred during the flight, this could impair your ability to concentrate, follow instructions, or react to the situation. This could seriously affect the safety of you and the people around you. Such incidents are rare but they do occur, and it can be fatal if you are unable to evacuate the plane properly (an example event is flight BA28M, where 55 people sadly died while the plane burned while sat on Manchester Airport runway, and the official AAIB incident report specifically commented on evacuation delays contributing to the deaths). No-one else on board a plane will evacuate for you – the cabin crew are there to guide an evacuation, but you need to be responsible for yourself. As a result, many airlines consider sedative medications as a reason why someone would not be allowed on a plane, in a similar way that someone who has consumed excessive alcohol may be removed from a plane.
Sedative drugs can make you fall asleep; however, the sleep is an unnatural non-REM sleep. Your movements during this type of sleep are reduced and this can place you at an even higher risk of developing blood clots in the legs (deep vein thrombosis – a DVT) or lungs (pulmonary embolism – a PE). These blood clots are very dangerous and can even be fatal. This risk further increases if your flight is over 4 hours long.
Going on an aeroplane normally involves your blood oxygen levels decreasing from around 98% to as low as 90%, due to the air pressure decrease at cruising altitudes. Normally your body compensates for this by altering the rate and depth of your breathing. However, benzodiazepines work to depress your breathing and this can put you at risk of hypoxia (excessively low blood oxygen), especially if you have lung problems already, which can be very dangerous.
Most people feel sleepy when they take Diazepam, but a small proportion of people experience the opposite effect and can become aggressive. This is called a paradoxical effect, and it can be unexpectedly inconsistent, even if Diazepam has been used in the past. Alongside aggression and agitation, this response can cause disinhibition and make you behave in ways you normally wouldn’t. This could also impact on your safety and the safety of your fellow passengers or could lead you to get in trouble with the law. Recently, a passenger in this situation was detained by the aircrew, arrested after an emergency landing, given jail time, and was also fined for the costs of redirecting the plane.
In several countries, Diazepam and similar drugs are illegal (Greece, Japan, and many Middle Eastern countries including the UAE are just some examples). They would be confiscated, and you might find yourself in trouble with the police for being in control of an illegal substance, even if it has been prescribed by a doctor in the UK. This has led to people spending time in a jail a foreign country.
Diazepam has a long half-life, which means it stays in your system for a significant time. If your job requires you to submit random drug testing, you may fail these tests.
There is a possible link between occasional use of benzodiazepines and earlier onset of dementia in later life.