Statistics show there were 545 drug abuse deaths recorded in 2009.
But Edinburgh University researcher Dr Roy Robertson said the total would be much higher if deaths from related diseases and violence were included.
He said: "I can imagine within the space of a few years we would see several hundred new cases added to the total."
Dr Robertson, who is also a GP in Muirhouse, Edinburgh, raised the issue at conference held by the Scottish Drugs Forum.
He pointed to official estimates that deaths from Hepatitis C contracted through drug injecting are expected to rise to 200 a year by 2014.
And he argued the overall total would be far greater if these fatalities were included, along with victims of other infections acquired through drugs, such as HIV and anthrax, and drug-fuelled violence and suicides.
"If we did include a larger number we would probably see several hundred more deaths and that trend would be upwards, because the trend in combined alcohol and drug use is greater than ever before," he said.
"You can't plan services, you can't structure your healthcare in any way if you don't know the size of the problem."
The conference in Glasgow will also hear how attempts are being made to cut fatalities through the use of naloxone.
The opiate is supplied in a pre-filled syringe and helps counteract the effects of a heroin overdose, providing more time for an ambulance to be called and treatment to be given.
It is being made available to drug users, their families and frontline workers through Scottish government funding.
The scheme has attracted controversy as critics claim it implies an acceptance of continuing drug use.
However Stephen Molloy, of the Scottish Drugs Forum, argued it can still be part of the recovery process, as well as helping save lives.
He said: "Ultimately someone may engage with services to receive naloxone and then perhaps be supported towards recovery.
"The reality is you can't recover if you are dead."
link to article on BBC website
link to video interview on BBC website