A transgender woman and her female friend were arrested for allegedly drugging a German tourist and stealing his holiday money in Thailand.

The ladyboy, Kritsana, 35, and her friend Suthasinee, 36, reportedly met the Bavarian visitor at a bar in Bangkok's red-light strip Sukhumvit Road and invited him back to his condominium for a threesome on June 26.

However, they spiked his drink with Alprazolam - a potent tranquiliser - and waited for him to fall unconscious before raiding his room for valuables, including cash, a credit card, and a camera.

Police Colonel Pongpichet Ninchan, commander of Sub-Division 3 of Tourist Police Division 1, said the German, who was not named in reports, filed a complaint with the Suvarnabhumi International Airport tourist police before returning to his home country.

He said: 'The victim filed a complaint at the Huamark Police Station, but the case has not progressed. We believe that this incident is a threat to society and harms Thailand's tourism image, so we ordered the Tourist Police investigation unit at the airport to search for the perpetrators.'

Police reviewed CCTV footage at the German's condominium and found the pair following him into his room on April 22.

The discovery led to the escorts' arrest. Officers found in their room 132 amphetamine pills, 3.74 grams of crystal methamphetamine, and 14 Alprazolam pills.

They allegedly confessed to drugging the tourist and said they spent his money to go partying and buy drugs.

Kritsana was also found to have a criminal history and had previously been arrested for a drug-related case.

Both women were charged with 'jointly committing robbery at night using a vehicle to take property away or to avoid arrest'.

Meanwhile, the German man thanked the police for apprehending the suspects and closing the case. However, he admitted that he would be reluctant to return to the country.

The incident comes after a Canadian tourist was allegedly robbed by two Ugandan prostitutes in Pattaya this June.

The Canadian, Khalid, reportedly paid the suspects, Mariam Nakayiza, 38, and Sheebah Ainembabazi, 28, to have drinks and a romp at his hotel room in Pattaya on June 10.

He told police he stripped off and lay on the bed, but fell asleep while receiving a rubdown from the women.

He allegedly woke up later only to find the escorts already gone, along with his safe containing 90,000 THB in Thai and foreign banknotes.

The Ugandan women, Mariam Nakayiza, 38, and Sheebah Ainembabazi, 28, have denied the charges.