Dictionary.com
Thesaurus.com

pothead vs. stoner

[pot-hed] / ˈpɒtˌhɛd /

noun

Slang.
  1. a person who habitually smokes marijuana.

[stoh-ner] / ˈstoʊ nər /

noun

  1. Slang. a person who is habitually high on drugs, especially marijuana, or alcohol; a person who is usually stoned.

  2. a person who pelts or assails with stones.

    stoners of Paul the Apostle.

  3. Chiefly British. a person or thing that weighs a specified number of stone (used in combination).

    a 12-stoner.