The amount of anti-depressant tablets slipped into the beer of a man who later died was at the lower end of the fatal range, a court heard.

Toxicology expert David Rose said the effect of somebody swallowing 27 Mirtazapine tablets, as Jason Wood did, would usually be dizziness, drowsiness and breathing problems.

Mixed with alcohol, he said, it would have “an added effect”. Mr Wood was nearly three times the legal driving limit when he died.

“With this amount of alcohol, taking on board that amount of Mirtazapine makes it much more dangerous,” said the senior scientific officer.

Maidstone Crown Court has been told that Mr Wood, who was 4ft tall and weighed six stone, had been drinking for several days at a house in Camden Square, Ramsgate, when Webster, 26, put the pills in his beer can “for a laugh” in October last year.

Mr Rose said another anti-depressant, Amitriptyline, was found in 30-year-old Mr Wood’s liver, though not his blood or urine, but added it was “nothing significant”.

There was a wide range of possible effects, he said, of Mirtazapine on the body.

Questioned by defence QC Oliver Saxby, Mr Rose said Amitriptyline was more toxic than Mirtazapine.

“Taken in higher levels than prescribed, it would be more likely to kill you,” he said.

The expert agreed that Mirtazapine was “relatively safe in overdose”, as it was often prescribed for patients who were suicidal. Manufacturers tried to mitigate the effect of an overdose.

Asked how many reported fatalities there were from Mirtazapine, Mr Rose said 10 had been quoted in literature. He agreed it was a small amount.

He also accepted he told police: “The Mirtazapine level in the blood just sneaks into the fatal range. Alcohol would have had an effect. It would have made the overdose more effective.

Webster, of Dover Road East, Gravesend, denies manslaughter and an alternative charge of administering poison or noxious substance as to endanger life.

The trial continues.