Лікар пояснив дозу й побічний ефект.

Лікар is in the nominative singular because it is the subject of the sentence: the person who performed the action.

• лікар = doctor
• In this sentence: The doctor explained...

A useful detail: лікар is a masculine noun, even though it ends in a consonant and not in -р specifically. Many masculine Ukrainian nouns end in a consonant.

Пояснив is the past tense, masculine singular form of the verb пояснити (to explain).

It agrees with the subject:

• лікар = masculine singular
• so the verb is пояснив

Compare:

• лікар пояснив = the doctor explained
• лікарка пояснила = the female doctor explained
• лікарі пояснили = the doctors explained

The dictionary form is пояснити, which is usually a perfective verb meaning to explain in the sense of completing the explanation.

So:

• пояснити = to explain, to make clear completely
• пояснив = explained

There is also an imperfective partner, пояснювати, which is used for repeated, ongoing, or habitual explanation.

Very roughly:

• Він пояснив = He explained / He has explained
• Він пояснював = He was explaining / He used to explain

Because Ukrainian nouns change form depending on their gender, declension pattern, and case.

Both words are in the accusative singular because they are direct objects of пояснив.

But they look different because they belong to different noun types:

• доза is a feminine noun ending in -а
  • nominative: доза
  • accusative: дозу
• побічний ефект is a masculine inanimate noun phrase
  • nominative: побічний ефект
  • accusative: побічний ефект
    For inanimate masculine nouns, the accusative usually looks the same as the nominative.

So the difference is normal and expected.

Because feminine nouns ending in -а usually change to -у / -ю in the accusative singular.

Examples:

• книга → книгу
• машина → машину
• доза → дозу

So after a transitive verb like пояснив, you use:

• пояснив дозу

Because ефект is a masculine inanimate noun, and in Ukrainian the accusative singular of masculine inanimate nouns is usually identical to the nominative singular.

So:

• nominative: побічний ефект
• accusative: побічний ефект

Compare this with an animate masculine noun, which often changes differently:

• nominative: лікар
• accusative: лікаря if it were a direct object meaning doctor

So inanimate vs. animate matters.

Й means and, just like і.

Ukrainian often alternates between і and й for euphony—to make the sentence sound smoother. After a vowel or in certain sound environments, й can sound more natural.

So:

• дозу й побічний ефект
• could also often be written as дозу і побічний ефект

Both mean the same thing. The choice is mainly about flow and pronunciation, not meaning.

Grammatically, it is singular:

• побічний ефект = a side effect / the side effect

If you wanted the plural side effects, you would use:

• побічні ефекти

So this sentence specifically mentions one side effect, at least grammatically.

Ukrainian does not have articles like English a/an/the.

That means:

• лікар can mean a doctor or the doctor
• дозу can mean a dose or the dose
• побічний ефект can mean a side effect or the side effect

The exact meaning depends on context.

No, Ukrainian word order is fairly flexible because case endings show the grammatical roles.

The neutral order here is:

• Лікар пояснив дозу й побічний ефект.

But other orders are possible, especially for emphasis:

• Дозу й побічний ефект пояснив лікар.
  Emphasizes that it was the doctor who explained them.
• Побічний ефект і дозу лікар пояснив.
  Can emphasize the things explained.

Even though word order can change, the cases still tell you what functions the words have.

It is grammatically clear, but depending on the intended meaning, a native speaker might sometimes phrase it differently.

For example, пояснити дозу can sound slightly unusual if the intended idea is explain the dosage/instructions rather than explain the dose itself. In real medical contexts, people might also say things like:

• Лікар пояснив дозування й побічні ефекти.
  = The doctor explained the dosage and side effects.
• Лікар пояснив, яку дозу приймати, і розповів про побічні ефекти.
  = The doctor explained what dose to take and told [the patient] about the side effects.

So your sentence is useful for grammar, but in real life the exact wording may vary.

A rough pronunciation guide:

• Лікар ≈ LEE-kar
• пояснив ≈ po-yas-NEEV
• дозу ≈ DO-zu
• й ≈ a short y sound, like the y in boy
• побічний ≈ po-BEECH-nyi
• ефект ≈ e-FEKT

Stress:

• лі́кар
• поясни́в
• до́зу
• побі́чний
• ефе́кт

Yes, sometimes.

Ukrainian past tense does not map perfectly onto English tense choices. Depending on context, пояснив can correspond to:

• explained
• has explained

Usually, in a simple sentence like this, explained is the most straightforward translation:

• Лікар пояснив дозу й побічний ефект.
  = The doctor explained the dose and the side effect.

The broader context determines whether English prefers simple past or present perfect.