John Mann, professor of chemistry at Queen's University, Belfast, also said the drug should have been banned sooner.
His comments came as it was disclosed up to 27 people in the UK may have died from taking mephedrone, which is also known as plant food and ''miaow miaow''.
Prof Mann, a fellow of the Royal Society of Chemistry, said the dangers of mephedrone could have been predicted because it was similar to other drugs.
Habitual users of khat, a drug popular in the Somali community, are known to suffer from impotence, he added.
He said: ''Could the dangers of this drug have been predicted? Of course they could.
''I think that the UK could have responded earlier because mephedrone is a very close structural analogue of cathinone - the major psychoactive ingredient of khat.''
''Mephedrone also has similar chemical structures to the amphetamines which are controlled substances with known dangers.''
On Monday Home Secretary Alan Johnson announced his intention to ban mephedrone and similar substances. The law is likely to be changed by April 16.
The Advisory Council on the Misuse of Drugs, which advises ministers on drugs, released its report on mephedrone on Thursday.
It said 18 deaths have been potentially linked to mephedrone in England, seven in Scotland and one each in Wales and Northern Ireland.
The report found mephedrone users tended to be younger than cocaine and ecstasy users, and were more often in their teens or 20s.
And it said police faced major difficulties in testing for mephedrone.
There is no simple street test and laboratory tests are expensive and time-consuming.
It said: ''Currently there is no simple drug field test available for cathinones. There is an urgent need to develop a simple and reliable field test.''
