impulsive

adjective

1. proceeding from natural feeling or impulse without external stimulus"an impulsive gesture of affection"
2. without forethought"letting him borrow her car was an impulsive act that she immediately regretted"
3. having the power of driving or impelling"a driving personal ambition"
4. determined by chance or impulse or whim rather than by necessity or reason"a capricious refusal"
5. characterized by undue haste and lack of thought or deliberation"a hotheaded decision"