Drink Spiking: It's illegal and can result in up to 10 years in prison. If it involves assault, rape or robbery the sentence will be higher.
Source: NHS Choices
Drink spiking is when a person adds a substance, such as drugs or alcohol, to anther person's drink without them knowing. It is usually difficult to detect whether or not a drink has been spiked as the look, smell and taste doesn't normally change.
If your drink has been spiked you are likely to feel and behave differently, and think that it's not right for the amount of alcohol you have drunk. Depending on what has been added to your drink you may be drowsy, confused, and find it difficult to move and even speak.
Try to avoid getting you drink spiked by:
Not accepting a drink from someone you don't know
Keeping your drink with you at all times, preferably in your hand
Drinking from a bottle rather than a glass so that you can keep your thumb over the top
Not sharing drinks
Not having valuables with you that might attract unwanted attention
Keeping a level of awareness of what's going on around you by not getting drunk.
If you think that your drink has been spiked tell a friend or someone you can trust, such as a pub landlord. Get yourself to a safe place and if you feel unwell ask a trustworthy person to take you to hospital. As soon as possible tell the police.