A leading neurophysiologist has cautioned that the long-term effects of the "miracle" anti-wrinkle treatment on the brain, nervous system and muscles are as yet unknown.

And Dr Peter Misra pointed out that Botox, a derivative of the deadly botulism toxin, could cause fatal muscular paralysis in its natural form and should be treated with care.

Side Effects

Writing in the British Medical Journal, he warned: "Robust evidence for the action of botulinium toxin (Botox) on sensory neurones is lacking."

He added that: "Animal experiments have shown that botulinium toxin affects the transmission of afferent nerves," and that the toxin "has been shown to play a part in inhibiting the release of neurotransmitters".

And Dr Misra pointed to a study published in 2001 that found 23% of patients seeking Botox treatment at a dermatology clinic had body dysmorphic disorder, and that psychotherapy was considered the more appropriate treatment for them.

But Dr Misra did point out in his article that "systemic side effects" of Botox treatment "are rare".

If side effects occur, they’re usually temporary starting within the first week, but may persist for several months. The kinds of side effects depend on where Botox is injected. For patients with frown lines, the most common side effects include

• headache
• respiratory infection
• flulike symptoms
• droopy eyelids
• nausea

Less frequent reactions include facial pain, redness at the injection site, and muscle weakness.