The police catch you with illegal drugs, and they quickly say you're not just being charged with possession. Instead, they're going to charge you with intent to distribute, which can bring about a stricter sentence.
Is it fair? How do the police know what you planned to do? If you maintain that you bought them for yourself and never planned to sell them, can they still charge you with intent to distribute?
They can, but they can't just work off of hunches. They need a reason to believe you were going to sell the drugs. This is when things can get tricky.
The first thing they'll look for is evidence that suggests sales were made. Maybe they found a briefcase full of cash in the car with the drugs. Maybe they found text messages on your phone that seem to suggest you were setting up meetings to sell to buyers. This type of evidence can then be entered into court.
Much of the time, the sheer amount of drugs you have can be used against you. Having a small amount suggests you were going to use the drugs yourself, whereas larger quantities suggest a sale was planned.
Is it fair? Not always. It's not illegal to have a large amount of cash in your car. The police could be reading too much into those text messages. Maybe you did buy the drugs for personal use, but you wanted to stock up, so you bought a lot at once -- or, perhaps you were with a group of people, and you were simply carrying the drugs for everyone else.
As noted, these cases can be complex, and they often rely on suggestions and surrounding evidence, rather than hard facts. Be sure you know what your defense options are if you think you're being charged unfairly.
Source: FindLaw, "Possession with the Intent to Distribute," accessed Aug. 23, 2017