No cocktails are usually recommended by a doctor if you are on a diet. This is because the alcohol and the drink usually contain a lot of calories and this would cause more problems for the person on the diet. Water is usually recommended for people to drink who are on a diet.
However, if a person wanted a cocktail, they should probably drink cocktails that are low in calories. These may be a vodka and water or a rum and diet coke.
Also, one cocktail won’t ruin a diet. However, drinking several cocktails especially those that are high in calories may ruin a diet. It is best to stay away from cocktail altogether when they are on a diet.