The American Psychological Association (APA) has endorsed gay marriage ahead of its annual convention in Washington.

With a unanimous 157-0 vote, the APA's policymaking body approved the resolution on Wednesday.

“Now as the country has really begun to have experience with gay marriage, our position is much clearer and more straightforward – that marriage equity is the policy that the country should be moving toward,” Clinton Anderson, director of APA's Office on Lesbian, Gay, Bisexual and Transgender Concerns, told USA Today.

The resolution notes that many gay men and lesbians “desire to form stable, long-lasting and committed intimate relationships and are successful in doing so.” And adds that campaigns to deny gay couples marriage equality “may have negative effects on their psychological well-being.”

Evan Wolfson, president of Freedom to Marry, cheered passage of the resolution.

“The American Psychological Association represents over 100,000 medical professionals who see day in and day out the real harms gay and lesbian people and their families experience when denied the freedom to marry,” Wolfson said in a statement. “With the freedom to marry in 12 countries on four continents, and most recently New York joining 5 other states plus the District of Columbia in ending exclusion from marriage, there is a mountain of unrefuted evidence and experience showing that extending the freedom to marry to loving, committed same-sex couples helps them and their families while hurting no one.”

The APA has filed 11 amicus briefs in support of marriage equality since approving a resolution on sexual orientation and marriage in 2004.

In 2009, the APA approved a resolution which repudiates “reparative” therapy, the controversial gay-to-straight treatment also known as “pray away the gay.”