Ryder returned a positive sample after being tested following a match for provincial side Wellington Firebirds against Northern Knights on March 24, the Sports Tribunal said in a release on its website (www.sportstribunal.org.nz/).
Ryder tested positive to 1-Phenylbutan-2-amine (PBA) and N, alphadiethyl-benzeneethanamine (DEBEA), both of which are banned in competition, and was subsequently handed a six-month provisional ban on April 19, the release said.
The tribunal issued a decision on Monday saying that it accepted Ryder's reasons for taking supplements and upheld the provisional ban, meaning the ban would be lifted on October 19.
"The mandatory penalty for this violation is two years' suspension," the tribunal said.
"However, the suspension can be less if the athlete establishes how the prohibited substances got in his system and that the taking of the prohibited substance was not intended to enhance his sport performance."
The tribunal added in its decision's notes: "We do not need to detail Mr Ryder's evidence other than to say in summary that he expressed a sensitivity arising from public comments about his weight and, as he was in a good space at the time about his cricketing form, he had decided to make a further attempt to reduce weight."
New Zealand's top anti-doping authority Drug Free Sport NZ (DFSNZ) said it had accepted the Tribunal's conclusion that 18-test batsman Ryder was not intending to enhance performance but added that he "had failed to heed clear warnings he had received".
"This is doubly disappointing as DFSNZ, NZ Cricket and the Cricket Player's Association had collaborated to institute an education programme for first class cricketers and Ryder had been part of that programme," DFSNZ CEO Graeme Steel said in a statement on the authority's website (www.drugfreesport.org.nz).
"Supplements are a minefield for athletes as, while benefits are invariably overstated, accurate information about contents and their status under sport rules is frequently insufficient."
The lenience of the decision and the lack of disclosure are likely to raise eyebrows in New Zealand, where Ryder's travails in a roller coaster career have been a constant source of controversy.
A burly lefthander who stepped away from test cricket last year to deal with personal issues, Ryder has struggled with weight problems throughout his career, along with alcohol and discipline issues.
Four days after being tested following his match for Wellington, Ryder was subject to a vicious assault outside a Christchurch nightspot which put him in hospital with critical head injuries.
He was expected to resume his provincial career with Otago later this year.
Doping cases have been relatively rare in cricket compared to other sports like athletics and cycling but a number of high-profile cricketers have failed drug tests.
Pakistan pacemen Shoaib Akhtar and Mohammad Asif, who is currently serving a seven-year ban for spot-fixing in a 2010 test against England, both tested positive for performance-enhancing drugs but had bans overturned on appeal.
Former Australia spinner Shane Warne was famously banned a day before the start of the 2003 World Cup in Africa and sent home after testing positive for a banned diuretic.