Impulse (Star Trek: Enterprise) - Trellium-D

Trellium-D is a fictional chemical substance from the Star Trek universe. It was introduced in the third season of Star Trek: Enterprise, and became an important recurring plot element throughout the season, exploring the subject of drug addiction.

Physical properties

Trellium-D was very rare; a similar but less useful mineral called Trellium-A was more common. With the right equipment, Trellium-D could be synthesized in a liquid state, but it was then very explosive, so the synthesizing procedures had to be followed exactly. Despite its volatility, Trellium-D was used in the mid-22nd century for starship insulation in the Delphic Expanse, as it offered protection against the region's dangerous spatial anomalies.

Physiological effects

It also had unusual properties affecting Vulcan physiology. In "Impulse," Trellium-D was revealed to be the cause of severe psychotic effects in that race, which led the crew of the Seleya to go insane and kill each other. Short-term exposure to the compound, which had been used by the Vulcan vessel as insulation, led to uncontrolled emotionalism on the part of Enterprise science officer, T'Pol, and Archer determined that it was too dangerous to use to protect his own vessel from the effects of the Expanse.

T'Pol suffered side-effects and flashbacks from her exposure to Trellium-D, but over the next few months found herself desiring to access more of the new emotions she experienced while under its influence. She secretly devised a way of liquefying small amounts of the compound which she injected directly into her bloodstream. The result was a level of increased emotions on her behalf, which initially were beneficial in her dealings with the crew. However, it also caused her to experience intense negative emotions, such as jealousy. In the episode "Azati Prime," T'Pol's emotions left her incapacitated as a commanding officer, contributing to the deaths of nearly two dozen Enterprise crew members in the ensuing Xindi attack.

In the following episode "Damage," T'Pol's addiction to Trellium-D reached breaking point when she nearly died trying to access some of the compound from a damaged part of the ship. She confessed her addiction to medical officer Dr. Phlox who treated her addiction and agreed not to reveal it to the captain.

Long-term exposure to Trellium-D was said to be damaging to Vulcan brains, and T'Pol's injecting of the chemical caused her permanent damage, to the extent that she was expected to have difficulty controlling her emotions for the rest of her life.