Some of the more commonly taken drugs are paracetamol and codeine, but if you suffer from a cough when you get a cold beware! Most of the cough medicines commonly available on the market contain alcohol, which could trigger in a breath alcohol test. There are numerous cases where this has occurred putting the driver, and the company they work for, in serious trouble.
Most people these days take the correct medicine to get better quickly; but always read the documentation that comes with the medicine. Some of the medicines state that you should not operate heavy machinery, and when it comes to heavy machinery there are few commercial vehicles that are not in that classification.
If you, or your staff, are driving under the influence of drugs, whether they are illegal, over the counter or prescribed drugs, and you have a collision then you stand a good chance of being prosecuted for driving whilst under the influence of drink or drugs.
The worrying part for business owners is that if that driver is your employee, and you do not have systems together with the appropriate procedures to ensure your employees are not driving under the influence, you may find yourself on the wrong end of a prosecution for permitting your employee to drive whilst under the influence.